Chlorofluorocarbons (hereinafter, CFCs) have been widely used as blowing agents for producing polymeric foams. However, the photolytic and homolytic reactivity at the chlorine-containing carbon sites has been shown to contribute to depletion of the earth's ozone layer. Additionally, the long atmospheric lifetime of CFCs has been linked to global warming. As a result, there has been a world-wide movement for over a decade to replace CFCs. (See “Montreal Protocol on Substances That Deplete the Ozone Layer,” Copenhagen Amendments, United nations Environment Program, 1992;
The characteristics sought in replacements to CFCs include boiling point ranges suitable for a variety of applications, low flammability, and low toxicity. One approach to developing CFC replacements has been to substitute hydrogen atoms for chlorine atoms so as to provide hydrochlorofluorocarbons (hereinafter, HCFCs) or hydrofluorocarbons (hereinafter, HFCs). HCFCs and HFCs have lower ozone depletion potentials (HFCs have zero ozone depletion potential) and shorter atmospheric lifetimes than CFCs. Unfortunately, HCFCs and HFCs are inferior to CFCs as foam blowing agents. (D. Rosbotham et al. in “HFC-134a—A Zero O.D.P. Option for Rigid Polyurethane Foam,” Proceedings of the SPI 34th Annual Polyurethane Technical/Marketing Conference, New Orleans, La. Oct. 21–24, 1992). The phase out of HCFC-141b has prompted many manufacturers of closed-cell, polyurethane foam to use alternative blowing agents.
Azeotropes and azeotrope-like con positions possess properties that make them useful foam blowing agents and solvents. For example, azeotropes and azeotrope-like compositions have a constant boiling point that avoids boiling temperature drift during processing and use. In addition, when an azeotrope or azeotrope-like composition is used as a foam-blowing agent, the properties of the foam can remain constant because the composition of the foam-blowing agent does not change during use. Azeotropes that are used as solvents also can be recovered conveniently by distillation.
Thus, there is a need for azeotropes or azeotrope-like compositions that are effective foam-blowing agents, and may also have good solvent strength, low flammability, are non-ozone depleting, and have a relatively short atmospheric lifetime so that they have a low global warming potential.